The graffiti was on Sutton's Beddington Farm Road, near to Ikea
A mural by graffiti artist Banksy has been defaced in south London while a public vote was taking place calling for its preservation.
Sutton Council asked residents to vote on whether the "punk" mural should stay on its Beddington Farm Road site.
More than 93% of the 250 voters urged the council to keep it but as the vote was taking place, the work was defaced by graffiti "taggers".
The council is deciding whether the mural can be restored.
The mural showed a punk standing by a box labelled IEAK - an anagram of the furniture store Ikea - apparently reading instructions on how to put together a graffiti slogan.
Despite usually operating a zero-tolerance stance on graffiti, the council made an exception for this piece of work.
The mural was defaced by "taggers" last month
Councillor Colin Hall said: "We believe in democracy and wanted local people to decide what should happen to the Banksy.
"Sadly someone decided to take it into their own hands."
He added: "The image actually criticised mindless graffiti so perhaps it isn't surprising that the sort of people who do that sort of thing should attack it."
The council is consulting the building's owner to decide whether the mural can be restored.
Acclaimed artist Banksy has gained an international following for his graffiti and exhibitions, the latest of which drew 300,000 visitors to Bristol earlier this year.
In September, Hackney Council in east London partially covered a Banksy mural with black paint by mistake.